In a tweet from the PlayStation support account, Sony stated, "We're aware that PSN is experiencing connectivity issues. Thank you for your patience as we investigate."
The PSN status page reveals that most services--including gaming, account management, and the PlayStation Store--are all affected to varying degrees. This means you may run into issues when trying to sign into PSN, access content on the store, play games, view your friends list, and so on.
PlayStation Video is also affected by today's issues, with PlayStation Now and PlayStation Vue are the only services to reportedly be working properly.
We'll be keeping an eye on the situation and will update this story with any further developments.